Iron-55

[2] The remaining 12% is accounted for by lower-energy Auger electrons and a few photons from other, minor transitions.

The advantages of the emitted X-rays are that they are monochromatic and are continuously produced over a years-long period.

[4] The ExoMars mission of ESA used, in 2016,[5][6] such an iron-55 source for its combined X-ray diffraction/X-ray fluorescence spectrometer.

[7] The 2011 Mars mission MSL used a functionally similar spectrometer, but with a traditional, electrically powered X-ray source.

[11] People close to the test ranges, for example Iñupiat (Alaska Natives) and inhabitants of the Marshall Islands, accumulated significant amounts of radioactive iron.